This invention relates to apparatus for modifying nuclear reactors and, more particularly, to an electro-mechanical apparatus for remotely locating, measuring and inserting plugs within coolant flow holes of a core barrel of a nuclear reactor.
A nuclear reactor 10, typical of the prior art, is shown in FIG. 1A as including a reactor vessel 16 into which is pumped a coolant fluid through an inlet 20 and, after cooling the reactor, to be discharged through an outlet 22. A core barrel 14 is disposed within the reactor vessel 16 and comprises a top former plate 12 and a baffle plate 32. As illustrated in FIG. 1A, the coolant flow is directed through an existing flow hole 26 downwardly along a path 34b and through an opening formed between the bottom of the baffle plate 32 and a lower core plate 18. A plurality of nuclear fuel rod assemblies 24, one of which is illustrated in FIG. 1A, is disposed within the core barrel 14. The coolant fluid is also directed downwardly along a path 34a and upwardly, as shown in FIG. 1A, through a plurality of openings 14a-14e formed within the bottom of the core barrel 14. Subsequently, the fluid directed into the core barrel 14 is directed upwardly through a plurality of openings 19a to 19d within a lower core plate 18 and, thereafter, directed about the plurality of nuclear fuel rod assemblies 24, thereby, removing heat therefrom.
In a nuclear reactor 10 of the downflow design, as shown in FIG. 1A, damage has been sustained to the fuel rods of the assemblies 24. Analysis indicates that the coolant flow, as directed along the path 34b and discharged through that opening formed between the baffle plate 32 and the lower core plate 18, impinges against and damages the fuel rods. To prevent nuclear fuel rod damage, it is proposed to convert a nuclear reactor from a downflow-type nuclear reactor 10, as illustrated in FIG. 1A, to an upflow-type reactor 10', as illustrated in FIG. 1B. Referring now to FIG. 1B, this conversion requires: (1) machining a plurality of new flow holes 28 within the top former plate 12, one such hole 28 being illustrated in FIG. 1B, and (2) plugging the existing flow holes 26 with plugs, one such plug 30 being illustrated in FIG. 1B. (Need a description of or reference to a description of the plugs 30?). The number of holes 26 and their location within the vertical wall of the core barrel 14 depends upon the particular type of nuclear reactor 10, i.e., whether the nuclear reactor 10 includes 2, 3 or 4 loops.
Referring now to FIG. 2, a core barrel 14 is illustrated as being submerged in canal water 40 filling a refueling canal 36 formed between canal walls 38a and 38b. The core barrel 14 includes a flange 66 disposed about its top-most edge. Due to the proximity of the core barrel flange 66 to the canal walls 38, the upflow conversion needs to be performed on the core barrel 14 while it is immersed within the refueling canal 36. As will be explained below, the apparatus of this invention serves to locate and measure the existing holes 26 within the core barrel 14, before inserting plugs 30 therein. It is imperative that these tasks be performed remotely in that there exists a high level of radiation adjacent to the core barrel 14 and the canal water 40.